Gapfill process using a combination of spin-on-glass deposition and chemical vapor deposition techniques

ABSTRACT

A method of filling a plurality of trenches etched in a substrate. In one embodiment the method includes depositing a layer of spin-on glass material over the substrate and into the plurality of trenches; exposing the layer of spin-on glass material to a solvent; curing the layer of spin-on glass material; and depositing a layer of silica glass over the cured spin-on glass layer using a chemical vapor deposition technique.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.10,431,031, filed May 6, 2003now U.S. Pat. No. 6,693,050, entitled“GAPFILL PROCESS USING A COMBINATION OF SPIN-ON-GLASS DEPOSITION ANDCHEMICAL VAPOR DEPOSITION TECHNQUES,” having Zhenjiang Cui et al. listedas inventors. This application is also related to U.S. application Ser.No. 10/430,942, filed May 6, 2003, entitled “MULTISTEP CURE TECHNIQUEFOR SPIN-ON-GLASS FILMS,” having Zhenjiang Cui et al. listed asinventors. The 10/431,031 and 10/430,942 applications are assigned toApplied Materials, Inc., the assignee of the present invention and arehereby incorporated by reference.

BACKGROUND OF THE INVENTION

One of the most popular techniques of isolating adjacent active devicesin modern integrated circuits is referred to as shallow trench isolation(STI). Such isolation techniques generally etch shallow trenches in thesilicon substrate, fill the etched trenches with a dielectric materialand then planarize the structure back to the silicon surface in theareas outside the trench. Active devices can then be built in the spacesor islands between the isolation regions.

FIGS. 1A-1D are simplified cross-sectional views of a partiallycompleted integrated circuit illustrating a common STI formation processformed on a silicon substrate 10. Referring to FIG. 1A, a typicalshallow trench isolation structure is created by first forming a thinpad oxide layer 12 over the surface of substrate 10 and then forming asilicon nitride layer 14 over pad oxide layer 12. The nitride layer actsas a hard mask during subsequent photolithography processes and the padoxide layer provides adhesion of the nitride to the silicon substrateand protects the substrate when the nitride layer is removed near theend of the STI formation process.

Next, as shown in FIG. 1B, a series of etch steps are performed usingstandard photolithography techniques to pattern the nitride and oxidelayers and form trenches 20 in silicon substrate 10. The photoresist(not shown) is then removed and a trench lining layer 16, such as an insitu steam generation (ISSG) oxide or other thermal oxide layer or asilicon nitride layer, is usually formed.

Referring to FIG. 1C, trenches 20 are then filled with an insulatingmaterial, such as gapfill silicon oxide layer 22, using a depositionprocess that has good gapfill properties. One or more additional stepsincluding chemical mechanical polishing (CMP) are then used to removenitride layer 14 and pad oxide layer 12 and level the gapfill oxide 22to the top of the trench (surface 24) as shown in FIG. 1D. The remaininginsulating oxide in the trenches provides electrical isolation betweenactive devices formed on neighboring islands of silicon.

Most integrated circuits include some regions that are isolated byrelatively narrow trenches, e.g., in the active areas 26 shown in FIGS.1B-1D, along with some regions that are isolated by much wider trenches,e.g., in open areas 28, that may be an order of magnitude or more widerthan trenches in the active areas. Additionally, the narrow-widthtrenches used in many integrated circuits have very high aspect ratiosmaking the filling of trenches 20 one of the most challenging gapfillapplications in the formation of the integrated circuit. The presence ofboth high-aspect-ratio, narrow-width trenches and relatively widetrenches in different parts of the silicon substrate make the filling ofthe trenches even more challenging.

A variety of different gapfill techniques have been developed to addresssuch situations. Despite the many successes achieved in this area,semiconductor manufacturers are continuously researching alternativetechniques to fill such gaps as well as improved techniques to fill theeven more aggressive aspect ratio gaps that will likely be required infuture processes.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the present invention deposit an insulating material thatcan be used to fill trenches or gaps between adjacent raised features.The techniques of the invention are particularly useful for fillingtrenches associated with shallow trench isolation structures inintegrated circuits but can be used in a variety of other applicationsincluding, but not limited to, the formation of premetal and intermetaldielectric layers in integrated circuits.

In one embodiment a method of filling a plurality of trenches etched ina substrate is disclosed. The method includes depositing a layer ofspin-on glass (SOG) material over the substrate and into the pluralityof trenches; exposing the layer of spin-on glass material to a solvent;curing the layer of spin-on glass material; and depositing a layer ofsilica glass over the cured spin-on glass layer using a chemical vapordeposition technique.

In another embodiment the method includes depositing a layer of spin-onglass material over the substrate and into the plurality of trenches;curing the layer of spin-on glass material by exposing the spin-on glassmaterial to electron beam radiation at a first temperature for a firstperiod and subsequently exposing the spin-on glass material to anelectron beam at a second temperature for a second period, where thesecond temperature is greater than the first temperature. The methodconcludes by depositing a layer of silica glass over the cured spin-onglass layer using a chemical vapor deposition technique.

These and other embodiments of the invention along with many of itsadvantages and features are described in more detail in conjunction withthe text below and attached figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1D are simplified cross-sectional views of a substrateillustrating a previously known shallow trench isolation formationprocess;

FIG. 2 is a flowchart depicting steps associated with one embodiment ofthe invention;

FIGS. 3A-D are simplified cross-sectional views of a substrate processedaccording to the sequence set forth in FIG. 2;

FIGS. 4A and 4B are simplified cross-sectional views of a substrate thatillustrate a potential problem associated with planarizing a substratehaving both SOG and CVD layers deposited within wide-width trenches whensolvent treatment step 54 of FIG. 2 is not employed;

FIG. 5 is a flowchart depicting steps associated with another embodimentof the invention;

FIG. 6 is a simplified cross-sectional view of a substrate havingnarrow-width trenches filled with SOG material according to theembodiment set forth in FIG. 5;

FIG. 7 is a simplified, cross-sectional view of an exemplary chamberthat can be used to perform electron beam radiation curing stepsdiscussed with respect to FIG. 5 in accordance with some embodiments ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention employ a combination of spin-on glass (SOG)and chemical vapor deposition techniques to deposit insulating material,such as silicon oxide material, in trenches and gaps between adjacentraised features. The inventors have developed methods of combining suchSOG and CVD deposition processes to complete STI structures in a mannerthat is superior to using either of SOG deposition or CVD techniquesalone.

In order to better appreciate and understand the present invention,reference is first made to FIGS. 2 and 3A-D. FIG. 2 is a flowchartdepicting steps associated with one embodiment of the invention as usedin a shallow trench isolation (STI) application while FIGS. 3A-D aresimplified cross-sectional views of a substrate processed according tothe sequence set forth in FIG. 2.

The process starts by depositing a spin-on glass (SOG) layer over asilicon substrate 30 (FIG. 2, step 50 and FIG. 3A). Referring to FIG.3A, prior to depositing the SOG layer, substrate 30 includes a pluralityof trenches suitable for forming a shallow trench isolation structure,such as trenches etched through a silicon/silicon oxide/silicon nitridestack as discussed above with respect to FIG. 1B. For convenience, thesame reference numbers are used in both FIG. 1B and FIGS. 3A-3C torepresent similar elements. Thus, the substrate shown in FIG. 3Aincludes a nitride layer 14 deposited over an oxide layer 12 which is inturn formed over the silicon substrate in areas outside the trenches.Also shown in FIG. 3A is a liner layer 16 formed within the trenches. Itis to be understood that embodiments of the invention are useful in anyshallow trench isolation technique regardless of the composition ofmaterials in the raised material stacks separated by the trenches andthat the invention is useful for spin-on dielectric materials other thanSOG.

The SOG material can be deposited using standard SOG depositiontechniques as is known to those of skill in the art. A number ofdifferent SOG precursors can be used in step 50 including precursorsavailable from Dow Corning, Honeywell and Air Products. The precursorshould be chosen to have, among other properties, gapfillcharacteristics and a dielectric constant suitable for STI applications.In one embodiment, FOx™, a flowable, inorganic polymer available fromDow Corning is used. FOx™ is a liquid solution of hydrogensilsesquioxane in a solvent that has a dielectric constant less than2.9, good gapfill properties and a low defect density.

As shown in FIG. 3A, deposition of the SOG material results in a partialfilling of the trenches including narrow-width, high-aspect-ratiotrenches 32 a and wide-width trenches 32 b with SOG 34. The SOG materialis effective at filling much of the narrow-width, high-aspect-ratiotrenches 32 a. It is generally not as effective at filling thewide-width trenches 32 b unless several or more applications, i.e.,layers, of the SOG material are applied sequentially. Also, even afterbeing cured, the SOG material has a higher number of undesirable Si—Sibonds than some CVD oxide films such as HDP-CVD oxide layers. Such Si—Sibonds are easy to oxidize into Si—O bonds and may result in uncontrolledchanges to film properties after the SOG film is deposited. Accordingly,embodiments of the invention address these issues by depositing an oxidelayer over the SOG material using chemical vapor deposition techniquesas described in detail below.

Prior to depositing the CVD oxide layer, embodiments of the inventionexpose the substrate and SOG material to a solvent (FIG. 2, step 52) inorder to dissolve some of the SOG material in the wide-width trenches.Referring to FIG. 3B, which is an enlarged view of area A shown in FIG.3A, the SOG material deposited in step 50 adheres to the sidewalls ofthe trenches creating a meniscus 35 a and 35 b in the narrow-width andwide-width trenches, respectively. The top of meniscus 35 a in thenarrow-width trenches 32 a is generally below the bottom of nitridelayer 14. The top of meniscus 35 b in the wide-width trench, however,contacts the sidewall of the trench at a point at or near the top ofnitride layer 14.

The inventors have determined that it is desirable to remove the SOGmaterial 34 from all areas above the bottom of pad oxide layer 12 priorto deposition of the CVD oxide layer. The SOG material and subsequentlydeposited CVD oxide film have different physical properties and thusdifferent wet etch rates and/or different planarization rates whenexposed to a CMP process. During subsequent planarization (FIG. 2, step58) of the substrate, the nitride and oxide layers 14 and 12 areremoved. The nitride and pad oxide layers have physical properties thatare similar to the CVD oxide layer and thus can be removed atapproximately the same rate allowing for a highly planarized surface tobe formed in step 58. If, however, the material removed during theplanarazation step included SOG material 34 in some areas of thetrenches and CVD oxide in other areas of the trenches, the differentremoval rates of these materials may result in an uneven surface.

This phenomenon is depicted in FIGS. 4A and 4B. In FIG. 4A, anindividual trench is filled above the bottom of pad oxide layer 12 withboth SOG material 34 and CVD oxide material 36. During a subsequentplanarization step, the SOG material has a higher WER than the nitridelayer 14, pad oxide layer 12 and oxide layer 36 which in turn results inan uneven surface 40 after the planarization step having concaved areas42 as shown in FIG. 4B.

Embodiments of the invention remove the meniscus portion of the SOGmaterial in the wide-width trenches by exposing the material to asolvent prior to curing the SOG material. The solvent dissolves some ofthe uncured SOG material including all or at least most of the materialthat is attached to the trench sidewalls above the bottom surface of thepad oxide layer as shown in FIG. 3B by dotted lines 35 c and 35 d. Inone embodiment the solvent is isopropyl alcohol (EPA) but it a varietyof other solvents may be used as can be determined by a person of skillin the art. In some embodiments, the solvent is a hydrophobic solutionbecause the SOG solution is also hydrophobic.

The solvent can be applied using spray and/or spin techniques as isknown in the art and is generally allowed to dry prior to curing the SOGfilm. The inventors have found that such a solvent treatment iseffective at removing the SOG material from the trench sidewalls abovethe pad oxide level while beneficially not removing much SOG materialfrom within the narrow-width trenches. Thus the solvent treatment doesnot adversely effect the gapfill capabilities of the SOG material in asignificant manner.

In one embodiment the solvent is applied sprayed on the substrate whilethe substrate is spun as is done in a traditional SOD deposition system.Spinning the substrate during and after application of the solvent helpsthe solvent dry faster. In one particular embodiment the substrate isnot heated during the solvent treatment step and it is spun at a rateless than 1000 rpm for one minute or less.

Referring to FIG. 3C, after solvent treatment step 52, the SOG materialis cured to remove hydrogen from the material (FIG. 2, step 54) and aCVD oxide layer 36 is deposited over the substrate (FIG. 2, step 56).The cure step generally causes dehydrogenation (Si—H+Si—H→Si—Si) andrearrangement/dehydration (—Si—H+—Si—O→—Si—O—H+—Si—;—Si—O—H+—Si—O—H→—Si—O—Si—+H₂O) of the SOG material resulting in Si—Siand Si—O—Si dominated bonding. The SOG material can be cured using astandard thermal cure step or by exposing the material to suitableradiation such as radiation from an electron beam. In other embodiments,however, the SOG material is cured in a multistep process as describedbelow with respect to FIG. 5.

CVD oxide layer 36 can be deposited using any appropriate CVD techniqueas is known to those of skill in the art. In some embodiments, however,CVD oxide layer 36 is deposited using high density plasma (HDP-CVD)techniques from a process gas of silane (SiH₄) and molecular oxygen(02). After deposition of CVD oxide layer 36, the substrate isplanarized (FIG. 2, step 58) to a planar surface 38 to remove thenitride and pad oxide layers and create the final STI structure as shownin FIG. 3D.

In another embodiment of the invention, the inventors developed amultistep cure technique that exposes the SOG film to radiation from anelectron beam. This embodiment is discussed in more detail inconjunction with FIG. 5, which is a flowchart depicting the stepsassociated with this electron beam cure technique and FIG. 6, which is asimplified cross-sectional view of a substrate having severalnarrow-width gaps filled in accordance with the process of FIG. 5. Theprocess shown in FIG. 5 starts with deposition of SOG material 72 oversubstrate 70 (step 60) and into trenched 74 as shown in FIG. 6,substrate 70 also includes a patterned nitride/oxide stack 14, 12 as wasshown in FIG. 1B.

Next, SOG material 72 is cured using a multistep electron beam radiationcuring process. A variety of different tools can be used to perform theelectron beam cure process. In one embodiment the ebeam cure is carriedout using a ebeam cure vacuum chamber similar to that described in U.S.Pat. No. 6,132,814, which is hereby incorporated by reference. Asimplified, cross-sectional view of such an ebeam cure chamber is shownin FIG. 7. As shown in FIG. 7, a substrate 102 can be placed in chamber100 and positioned underneath an electron source 104. The chamber can beevacuated to a pressure between, for example, 15-40 millitorr with avacuum pump 106. The electron source can be any source that works insuch a vacuum environment. One example of a suitable electron sourcewhich generates a large uniform and stable source of electrons isdescribed in more detail in U.S. Pat. No. 5,003,178, which is herebyincorporated by reference.

Electron source 104 includes a cathode 110 and an anode 112 separated byan insulating member 114. The potential between these two electrodes isgenerated by a high voltage supply 116 applied to the cathode and a biasvoltage supply 118 applied to the anode. The temperature of substrate102 can be controlled during the ebeam curing process by quartz lamps120 that irradiate the bottom side of the substrate to provide heatindependent of the electron beam.

The multistep ebeam curing process starts by transferring the substrateto ebeam cure chamber 100 and exposing it to electron beam radiation ata first, relatively low temperature (step 62). In one embodiment curestep 62 exposes the substrate to an electron beam at room temperaturefor about three minutes by not heating the substrate with the quartzlamps. During this portion of the ebeam cure step the substrate isheated above room temperature by the ebeam (e.g., to a temperature ofbetween 70-200° C.) but little or no additional heating of the substrateoccurs.

The amount of energy used during the ebeam radiation step is selected tobe sufficient for the electrons to reach the bottom of the trench. Theinventors have found that exposure to ebeam radiation at such relativelylow temperatures allows the electrons to penetrate further into SOGmaterial 72 than if a relatively high temperature is initially used. Theuse of too high a curing temperature during step 62 may result in theformation of a crust of cured SOG material on the upper surface of theSOG material in the trenches. The early occurrence of such crustingimpairs electron penetration into the trenches thus making it difficultto adequately cure the SOG material all the way down to trench bottoms.

Next, the temperature of the substrate is increased with the quartz lampheater (or by other means) and the substrate is exposed to additionalelectron beam radiation at the increased temperature (FIG. 5, step 64).In one embodiment, cure step 64 exposes the substrate to an electronbeam at a temperature between 350-450° C. for about three minutes duringstep 64. In some embodiments, there is at least a 50° C. difference insubstrate temperature between steps 62 and 64 while in other embodimentsthere is at least a 150° C. difference in temperature.

In one embodiment both curing step 62 and 64 are performed in anozone/oxygen environment in order to create more O—Si—O bonds and lessSi—Si bonds. In other embodiments, the curing can be performed in aozone/oxygen/inert gas ambient or in just an inert gas ambient, however.In one particular embodiment cure step 62 exposes the SOG material to anelectron dose of 16 keV and 3750 uC/cm at 195° C. (the temperature thesubstrate reaches without additional heating from the quartz lamps) andthen exposes the SOG material to the same electron dose at a temperatureof 400° C. by switching on the quartz lamp heater during step 64.

Experiments performed by the inventors have determined that such atwo-step curing technique is superior to both conventional thermalcuring processes and to ebeam curing techniques that use a single step.In other embodiments, more than two discrete ebeam cure steps may beused. For example, in one embodiment step 62 is divided into two steps62 a and 62 b where the electron dose is increased from a first level toa second level from step 62 a to step 62 b. In another embodiment anintermediate step, between steps 62 and steps 64, is performed in whichthe substrate is heated to a temperature higher than done in step 62 butlower than done in step 64. In other embodiments four or more discreteebeam cure steps may be employed.

In some embodiments, the multistep cure technique shown in and discussedwith respect to FIG. 5 can be used in place of cure step 54 in FIG. 2.In other embodiments, however, the cure technique disclosed in FIG. 5can be used to form an SOG gapfill film independent of the solventtreatment step and CVD deposition steps shown in FIG. 2. After the SOGlayer is cured, a CVD oxide layer is deposited over the substrate (FIG.5, step 66) and the substrate is planarized (FIG. 5, step 68).

Additional embodiments of the invention add an oxygen plasma treatmentstep after either SOG cure step 52 or steps 62, 64 and prior to thedeposition of a CVD oxide layer. The oxygen plasma treatment stepexposes the cured SOG material to an in situ plasma formed frommolecular oxygen or another oxygen source in order to further oxidizethe SOG material and convert as many remaining Si—Si bonds as possibleto Si—O bonds. In one embodiment the oxygen plasma treatment exposes thesubstrate to an oxygen plasma formed in a Ultima HDP-CVD chambermanufactured by Applied Materials, the assignee of the presentinvention, for between 0.5-10 minutes.

Still other embodiments of the invention apply and cure multiply layersof SOG material prior to depositing the CVD oxide layer. For example, inone embodiment, a layer of SOG material is deposited over the substrateto partially fill about one quarter of the height of the narrow-widthtrenches. If appropriate, the SOG material is then exposed to solventprior to being cured to remove SOG material from the wide-widthtrenches. Next, a second layer of SOG material is formed toapproximately halfway fill the narrow-width trenches. Again the materialis exposed to the solvent, if appropriate, and cured. The remainder ofthe trenches can then be filled with a CVD oxide as disclosed above.

The description above has been given to help illustrate the principlesof this invention. It is not intended to limit the scope of thisinvention in any way. A large variety of variants are apparent, whichare encompassed within the scope of this invention. While the inventionhas been described in detail and with reference to specific examplesthereof, it will be apparent to one skilled in the art that variouschanges and modifications can be made therein without departing from thespirit and scope thereof. These equivalents and alternatives areintended to be included within the scope of the present invention.

1. A method of filling a gap formed between adjacent raised surfaces ofa substrate, the method comprising: depositing a layer of spin-on glassmaterial over the substrate and into the gap; exposing the layer ofspin-on glass material to a solvent; curing the layer of spin-on glassmaterial; and depositing a layer of silica glass over the cured spin-onglass layer using a chemical vapor deposition technique.
 2. The methodof claim 1 wherein the chemical vapor deposition technique is a plasmaCVD process.
 3. The method of claim 2 wherein the plasma CVD process isa high density plasma CVD process that includes simultaneous sputter anddeposition components.
 4. The method of claim 1 wherein the spin-onglass material is cured using radiation in the form of an electron beam.5. The method of claim 1 wherein the spin-on glass material is curedusing process comprising: exposing the spin-on glass material to anelectron beam during a first period; and thereafter, increasing atemperature of the substrate and exposing the spin-on glass material toan electron beam during a second period.
 6. The method of claim 5wherein the solvent comprises isopropyl alcohol.
 7. The method of claim5 wherein the temperature of the substrate is increased by at least 50degrees Celsius between the first period and the second period.
 8. Themethod of claim 5 wherein the temperature of the substrate is increasedby at least 150 degrees Celsius between the first period and the secondperiod.
 9. The method of claim 1 wherein the spin-on glass material isdeposited from a liquid precursor solution comprising hydrogensilsesquioxane.
 10. The method of claim 1 wherein the spin-on glassmaterial partially fills the gap.
 11. The method of claim 10 wherein thespin-on glass material has a dielectric constant of less than 2.9. 12.The method of claim 11 wherein the layer of silica glass deposited witha chemical vapor deposition technique completely fills the gap.
 13. Themethod of claim 1 wherein the solvent is applied to the substrate usinga spray or spin-on technique.
 14. The method of claim 1 wherein thesolvent is allowed to dry prior to curing the layer of spin-on glassmaterial.
 15. The method of claim 1 wherein the substrate is not heatedwhile the solvent is applied.
 16. The method of claim 1 furthercomprising depositing a second layer of spin-on glass material over thesubstrate and into the gap prior to depositing the layer of silica glassusing a chemical vapor deposition technique.
 17. A method of filling aplurality of gaps formed between raised surfaces of a semiconductorsubstrate, the plurality of gaps including a plurality of closely-spacedgaps formed in an active area of the substrate and at least gap formedin an open area of an integrated circuit being formed on the substrate,where a width of the gaps in the open area is significantly wider than awidth of at least some of the plurality of closely-spaced gaps in anactive area of the integrated circuit, the method comprising: depositinga layer of spin-on glass material over the substrate such that it atleast partially fills the plurality of gaps; exposing the layer ofspin-on glass material to a solvent; curing the layer of spin-on glassmaterial; and depositing a layer of silica glass over the cured spin-onglass layer using a high density chemical vapor deposition techniquethat includes simultaneous deposition and sputter components.
 18. Themethod of claim 17 wherein the spin-on glass material is cured usingprocess comprising: exposing the spin-on glass material to an electronbeam during a first period; and thereafter, increasing a temperature ofthe substrate and exposing the spin-on glass material to an electronbeam during a second period; wherein the temperature of the substrate isincreased by at least 50 degrees Celsius between the first period andthe second period.
 19. The method of claim 17 wherein the gaps areformed in a silicon substrate having one or more dielectric layersformed thereon such that the plurality of gaps form islands therebetween, the islands comprising an upper strata of dielectric materialand a lower strata of silicon and wherein the solvent treatment stepremoves spin-on glass material from sidewalls of gaps in the open areasuch that any remaining spin-on glass material in the gaps in the openarea is below the upper strata of dielectric material and wherein themethod further comprises planarizing the shallow trench isolationstructure down to the lower silicon strata.
 20. The method of claim 17wherein the spin-on glass material is deposited from a liquid precursorsolution comprising hydrogen silsesquioxane.
 21. The method of claim 17further comprising exposing the cured spin-on glass layer to an oxygenplasma prior to depositing the silica glass layer.